1. Field of the Invention
The present invention relates to a battery or electrochemical storage cell, in particular a secondary cell, containing at least one electrode prepared from at least one electrically conductive and electrochemically oxidizable and/or reducible polymer. The battery or electrochemical storage cell of the present invention can be at least substantially free, or completely free, of metal components.
2. Description of the Related Art
Since the discovery that polymeric materials, and in particular polyacetylene, could be reversibly doped and undoped and thus employed as electrode materials for charge storage applications, much consideration and investigation has been directed towards employing polymers in a wide variety of electrical and electronic device applications, including energy storage (R. B. Kaner et al., J. Phys. Chem., 90, 5102 (1989); K. Kaneto et al. Japn. J. Appl. Phys., 22, L567 (1983)), light emitting diodes (D. Braun et al., Appl. Phys. Lett., 58, 1982 (1991); J. J. M. Halls et al. Nature, 376, 498 (1995); M. Granstrom et al., Science, 267, 1479 (1995)), sensors (J. W. Thackeray et al., J. Phys. Chem., 89, 5133 (1985); G. Fortier et al., Biosensors and Bioelectronics, 5, 473 (1990); P. N. Bartlett et al., J. Electroanal. Chem., 224, 27 (1987)), and electrochromic devices (H. Yashima et al., J. Electrochem. Soc., 134, 46 (1987); M. Gazard, Handbook of Conducting Polymers, Vol. 1, ed. (1983)).
The conductivity of neutral polymers can be dramatically increased by chemically doping the polymers in a controlled manner with electron acceptor and/or electron donor dopants. The term doping used in connection with conducting polymers refers to the partial oxidation (p-doping) or partial reduction (n-doping) of the polymer, combined with the associated transport of charge compensating dopant ions into or out of the polymer. Conducting polymers are characterized by their ability to be switched between a neutral (or insulating) state and one or more doped (conducting) state(s).
In charge storage applications, such as electrochemical secondary storage cells, electrode materials should be able to undergo multiple doping and undoping cycles with high utilization efficiency and chemical stability. In addition, the two electrode materials should have a high charge capacity and combine to exhibit a high cell voltage.
Polyacetylene, polypyrrole, polyaniline, polythienylene, and polythiophene are among the several polymers that have been investigated and drawn intense interest to date in connection with charge storage applications. For example, a polymeric storage cell with a polypyrrole (cathode) electrode and polypyrrole/polystyrene sulfonate (anode) electrode is described in U.S. Pat. No. 5,637,421 to Poehler et al., the complete disclosure of which is hereby incorporated by reference.
However, repeated doping and undoping during charging and/or discharge may cause degradation of the polymer. Many polymers, such as polyacetylene, have been plagued by poor charge/discharge cycling characteristics (i.e., reversibility) due to inferior chemical and electrochemical stability. For instance, while improvement in charge capacity and reversibility has been reported in connection with the p-doping of poly(3(4-fluorophenyl)thiophene), this polythiophene derivative exhibits relatively low charge capacity and poor reversibility when n-doped.
Thus, while some progress has been made in understanding conduction mechanisms, electronic structure, doping characteristics, and optical properties in conductive polymers, there remains the need to develop improved polymeric electrodes for electrochemical storage cells that exhibit suitable charge capacities and reversibilities in both the n-doped and p-doped states and can be employed in commercial applications without the need for metallic components.